Electrical stimulation of peripheral nerves of isolated pleural-pedal ganglia, an in vitro analogue of long-term behavioral training in Aplysia, produced changes in the synthesis of specific proteins in pleural sensory neurons. The changes in incorporation of [35S]methionine into proteins occurring 24 h after electrical stimulation (late) were determined and compared with changes occurring immediately after stimulation (early). Eight proteins were affected 24 h after electrical stimulation. Three of these proteins were also affected immediately after electrical stimulation. Two of the proteins affected late are components of the cytoskeleton. One protein was identified as actin. The other protein was purified from preparative 2D-gels and partial amino acid sequences of 3 peptides derived from this protein were determined. The peptide sequences were found to be identical to those of an Aplysia intermediate filament protein.